make sure list predicates are available to whoever needs them.

pl/lists.yap

@@ -0,0 +1,24 @@
+%   memberchk(+Element, +Set)
+%   means the same thing, but may only be used to test whether a known
+%   Element occurs in a known Set.  In return for this limited use, it
+%   is more efficient when it is applicable.
+
+lists:memberchk(X,[X|_]) :- !.
+lists:memberchk(X,[_|L]) :-
+	lists:memberchk(X,L).
+
+%   member(?Element, ?Set)
+%   is true when Set is a list, and Element occurs in it.  It may be used
+%   to test for an element or to enumerate all the elements by backtracking.
+%   Indeed, it may be used to generate the Set!
+
+lists:member(X,[X|_]).
+lists:member(X,[_|L]) :-
+	lists:member(X,L).
+
+lists:append([], L, L).
+lists:append([H|T], L, [H|R]) :-
+	lists:append(T, L, R).
+
+
+